The present invention relates to an improved transmission of the type including a combination of hydrostatic (fluid) and mechanical devices. More specifically, the present invention related to a transmission that may transmit power solely through the hydrostatic portion of the transmission, solely through the geared portion of the transmission or in combination through both the hydrostatic and geared portion of the transmission.
Both hydrostatic transmissions and geared transmissions are used in agricultural and construction equipment to transmit power from power sources, such as internal combustion engines to equipment for accomplishing a desired task. For example, transmissions are used to properly transmit power to the wheels of a vehicle, or to a vehicle implement. Two important considerations in selecting transmissions are their efficiency and range of input and output speed variability. In general, hydrostatic transmissions provide extremely high-speed variability between the input and output, but are less efficient than geared transmissions. Unlike construction equipment applications, the agricultural applications require prolonged operation at full power in the xe2x80x9ctillagexe2x80x9d or xe2x80x9cworkingxe2x80x9d speed range. Under these conditions, optimum efficiency is required. Further, xe2x80x9con roadxe2x80x9d haulage performance requirements similar to that of a truck is desired for operating the work vehicle on the highway. In certain instances, it is required that the work vehicle has the capability of maintaining a road speed of 50 km per hour.
In an agricultural equipment application, such as on a tractor, power to drive an implement is typically obtained from a power take-off (PTO) device that is coupled to the tractor""s primary power source or engine. When the tractor is using the PTO, the engine speed must be held constant to maximize the efficient use of the implement. With a conventional transmission, such situation cannot be maintained if the tractor speed changes since that will affect the PTO""s rpm and therefore affect the implement""s efficiency.
Thus there is a need for a transmission for use with agricultural equipment that will provide a constant horsepower with the ability to change speed and torque in a seamless manner, in other words, xe2x80x9ccontinuously variablexe2x80x9d. There is also a need for a continuously variable hydro-mechanical transmission that provides a xe2x80x9cworking rangexe2x80x9d for tillage and heavy draw bar applications and a xe2x80x9crouting rangexe2x80x9d for haulage and transport on the highway.
The present invention provides a continuously variable hydro-mechanical transmission. The transmission includes a transmission housing and a hydrostatic power unit associated with the housing. The hydrostatic power unit includes a pump coupled to a motor with the hydrostatic power unit coupled to a first input shaft and a first output shaft. The hydrostatic power unit is selectively coupled to a synchronous lockup clutch with the first output shaft, wherein a hydrostatic input speed range is selected. A compound planetary gear unit is mounted in the housing with the compound planetary gear unit including a second input shaft, a third input shaft, a fourth input shaft and a second output shaft. The compound planetary gear unit is selectively coupled to the load, selectively coupled to the hydrostatic power unit and coupled to the power source. A load shaft coupled to the load and mounted for rotation in the housing is selectively coupled to the compound planetary gear unit through an intermediate shaft supporting a range gear set mounted for rotation in the housing and selectively coupled to the compound planetary gear unit and the load shaft.
The present invention also provides a compound planetary gear unit which includes a primary sun gear coupled to the second input shaft, a secondary sun gear coupled to the third input shaft with the third input shaft selectively coupled to the first output shaft with the synchronous lockup clutch. A ring gear is coupled to the fourth input shaft and is selectively coupled to the first output shaft also with the synchronous lockup clutch. A compound planetary gear cluster, preferably composed of three compound planetary gears, is mounted on a compound planetary gear carrier which engage with the secondary sun gear and the ring gear, with the compound planetary gear carrier coupled to the second output shaft. A hydrostatic disconnect clutch is coupled to the first output shaft wherein the hydrostatic power unit can be disconnected from the compound planetary gear unit, thereby providing a pure mechanical power transmission from the power source directly to the primary sun gear within the compound planetary gear unit. With the hydrostatic power unit coupled to the compound planetary gear unit, a hybrid hydro-mechanical power input from the power source and the hydrostatic power unit can be conveyed to the load through the compound planetary gear unit in a seamless manner within a work range and a road range as selected by the operator of the continuously variable hydro-mechanical transmission.
The present invention further provides a continuously variable hydro-mechanical transmission comprising a transmission housing with a hydrostatic power unit associated with the housing and a compound planetary gear unit mounted in the housing. The hydrostatic power unit includes a pump coupled to a motor with the hydrostatic power unit selectively coupled to a first input shaft and having a first output shaft. The compound planetary gear unit includes a second input shaft, a third input shaft, a second output shaft and a third output shaft. The compound planetary gear unit is selectively coupled to the load, coupled to the hydrostatic power unit and selectively coupled to the power source. The compound planetary gear unit can be connected to a plurality of range gear sets. The plurality of range gear sets are mounted for rotation on an intermediate shaft in the housing and selectively coupled to the compound planetary gear unit and a load shaft. The load shaft is coupled to the load and mounted for rotation in the housing.
The compound planetary gear unit comprises a primary sun gear coupled to the second input shaft. A ring gear is coupled to the third input shaft and coupled to the first output shaft with the hydrostatic power unit. A secondary sun gear is coupled to the third output shaft and a compound planetary gear cluster mounted on a compound planetary gear carrier is engaged with the primary sun gear, the secondary sun gear and the ring gear. The compound planetary gear carrier is coupled to the second output shaft. In this configuration, with two inputs to the compound planetary gear unit and two output shafts from the compound planetary gear unit, an operator can select a hybrid hydro-mechanical input from the power source and the hydrostatic power unit or the operator can disconnect the power source from directly driving the compound planetary gear unit and thereby provide a pure hydrostatic power input to the compound planetary gear unit. The plurality of range gear sets operate with synchronized shift points, which provide seamless speed changing from zero to a maximum speed based on the range selected by the operator including combinations of range gear sets as selected by the operator.
The present invention also provides the hydro-mechanical transmission comprising a differential, such as a compound planetary gear arrangement, which includes a first input shaft, a second input shaft and an output shaft, wherein the torque and speed on the output shaft are a function of the torque and speed of the input shafts. A power source, such as an engine, is coupled to the first input shaft and a hydraulic motor is coupled to the second input shaft. A hydraulic pump is hydraulically coupled to the hydraulic motor and powered by the engine. A range transmission, such as a range gear set, including an input transmission shaft and a transmission output shaft is configured to permit selection of at least two speed ratios between the transmission input and output shafts. The range transmission input shaft is coupled to the output shafts of the differential. A multi-speed transmission including a driven shaft and driving shaft is coupled to the transmission output shaft. The multi-speed transmission is configured to permit selection of at least three speed ratios between the driven shaft and the driving shaft. The driving shaft of the multi-speed transmission may be the same as the output shafts of the differential and the input transmission shafts of the range transmission may also be the output shafts of the differential.
The present invention also provides a hydro-mechanical transmission comprising a differential including a first input shaft, a second input shaft and an output shaft, wherein the torque and speed of the output shaft are a function of the torque and speed of the input shafts. A power source or engine is coupled to the first input shaft. A range transmission including a transmission input shaft and a transmission output shaft are coupled to the second input shaft of the differential, wherein the range transmission is configured to permit selection of at least two speed ratios between the transmission input and output shafts. A hydraulic motor is coupled to the transmission input shaft and hydraulic pump is hydraulically coupled to the hydraulic motor and powered by the power source or engine. The differential can be a compound planetary gear arrangement or unit. The transmission can also include a multi-speed transmission coupled to the output shaft of the differential.